NodeBB connection has been lost, attempting to reconnect

Hi,
I paid somebody to install nodebb for me and all was going fine, i had a subdomain setup on my site so it would point to my vps with nodebb installed on it. Everything was fine until I tried to post another post and It told me that connection had been lost. I've tried restarting it multiple times and it still won't work.

Thank you very much @PitaJ . now it is ok. but i remember that i had same problem two days ago after configure ngnix and config. site was good also i entered some categories and soon suddenly i got above errors. i hope it wont give error again.